The protocol used specifically for the exchange of emails is

SMTP is the protocol built specifically to send and relay email between mail servers.

TCP is a general transport protocol that merely carries the mail data underneath SMTP.

IP only addresses and routes packets and does not manage email exchange.

None of the above is wrong because SMTP is precisely the email-sending protocol.

Receiving clients typically pull mail using POP3 or IMAP after SMTP has delivered it.

SMTP normally listens on port 25 for server-to-server mail transfer.